Due to small mode sizes in photonic waveguides, specially designed optical couplers are required to couple light to and from an integrated photonics chip. Owing to tight alignment tolerance, active alignment is typically utilized during packaging and assembly of lasers and fibres with integrated photonics chips. As part of the active alignment process, an optical power monitor is typically used for determining optimal alignment position. In silicon photonics, a typical method of implementing an optical power monitor on chip is by using a power splitting device such as a directional coupler to tap a small percentage of coupled light from an input waveguide. This small percentage of light that is tapped is then sent to an on-chip monitor photodetector. Disadvantageously, the directional coupler tapping percentage is wavelength dependent and sensitive to fabrication variations. Directional couplers are also polarization sensitive. Furthermore, the small percentage of light that is tapped from the input waveguide also results in optical loss. It is therefore desirable to provide a scavenging photodetection device that mitigates these drawbacks.